Thanks Rolf for refreshing my feeble brain.  The ~r in the UDG does indeed pick up the content of the user default reply-to address.  I now remember configuring it this way because I use MercD to POP hosted mailboxes and could not use ~8 because the local account names and hosted account names are different.

I just added a new user in Mercury then installed Pegasus Mail on a WinXP workstation using wssetup.exe.  I configured PMail as normal but sent messages show a From header that is missing the email address part (From: "username"<>).  Adding a default reply-to address solved the problem but I don't recall that being required before.  I checked the pmail.ini file of several other users and all contain a default reply-to address entry so I must have been entering one all along and forgot this time around.  The Pegasus help file and manual both say a default reply-to address is needed only if you want a different reply-to address.  Is it normal that a default reply be required in my environment or do I have a configuration issue that the default reply-to resolves?

12 users, Mercury 4.74, Pegasus Mail 4.63, Server2003, WinXP & Win7 workstations.

This is probably what you are looking for (from Pegasus help):

The following items can be changed in the Basic Settings preferences page:

Personal name  Pegasus Mail attaches whatever you enter here to your address when you send messages, making it easier for the recipient to identify who you are. You should make this entry simple and clear. Your personal name should consist only of letters and digits.

That is how I got the From field content of: "username"<>.  I probably should have shown it as: "PersonalName"<>. 

The piece that is missing is the email address.

Ah, I thought it was the other way around, my mistake. In that case it's probably this setting that needs to be added:

General Internet mail settings

My Internet e-mail address is  Enter your electronic mail address here. Your electronic mail address will usually be in the form username@host.domain - enter the whole address here 

That one is there as well.  It was populated during workstation setup.

Could there be something wrong with the "Reply address format" setting in the UDG that could be causing the problem?  Mine looks like: "~p"<~r>

 "~p"<~r> indicates Personal name / Reply to: address. Alternatively account name and domain name can be specified ("~p" <~8@host.domain>). I don't think it should make any difference for the From header, though.